1. Field of the Invention
The present invention relates to a modem, and more particularly, to a method and apparatus for monitoring the line conditions between modems transmitting data in the data mode.
2. Description of the Related Art
A modem is a signal converting device that allows a computer system to communicate with other computer systems or other electronic systems over a network such as a telephone network. Because telephone systems were originally designed to carry modulated analog voice signals, today""s telephone networks do not allow direct digital current signals to pass between computer systems. Thus, a modem can be used to convert the direct current pulses of the digital code from the computer system to an analog signal that is capable of being transmitted over a telephone network.
Uniform modem operating standards allow computer systems to communicate with each other over a world-wide telephone network. One organization for setting such standards is the International Telecommunications Union Telecommunications Standards Sector (ITU-T), a United Nations organization formerly known as the Comitxc3xa9 Consultatif International Telegraphique et Txc3xa9lxc3xa9phonique (CCITT). Over the years, the standards established by ITU-T have improved in the amount of data that can be transferred over a telephone network in a given period of time. An earlier ITU-T standard, V.22, allows a transfer rate of 1200 bits per second (bps). The V.32 standard allows a data transfer rate of up to 9600 bps. The V.32bis standard extends the V.32 standard to 14,400 bps. Under the V.34 standard, modems can transfer data at rates as high as 28,800 bps.
A connection between two modems over a computer network is established by a call progressing protocol or startup procedure. After dialing the answering modem and receiving a ringing tone, the calling modem assumes that a connection is made with the answering modem if no busy signal is received from the answering modem. The calling modem then sends out various tones at different frequencies and adjusting signals to the answering modem. The answering modem analyzes the received tones and signals to determine the conditions of the line. Similarly, the answering modem sends out the same type of tones and signals as well. During these training phases, both modems adjust their channel compensation modules to compensate for or adjust to the conditions of the telephone network. When the channel compensation modules are well trained, or set for the maximum amount of data transfer, the modems then proceed into the data mode where data from the computer systems can be transferred between the modems over the telephone network.
One problem in transmitting data over the telephone network is that changing line conditions in the telephone network decrease the amount of data that can be transferred over a given period of time. Some of these conditions include cross talking, interference from other sources such as power lines, and changing weather conditions.
In order to compensate for changing line conditions, the channel compensation modules need to be reset or retrained. Retraining is invoked when one of the modems detects an unsatisfactory signal reception or detects a certain tone signal from the other modem. However, the approach of waiting until line conditions become unsatisfactory can delay entering the retraining mode. During such a delay, the line conditions may change so rapidly as to cause a disconnection between the two modems. A disconnection requires a computer system to redial the other modem and reestablish a connection. Besides the extra time involved, some computer network providers charge a fee for the initiation of a new call. Furthermore, in some high traffic areas such as a popular internet site, reestablishing a connection may take several minutes if not hours.
Some past methods for detecting unsatisfactory signal reception include implementing CRC error correction which requires that the modems be compatible with the V.42 standard and monitoring the average noise of a connection for a given period of time which requires additional hardware in the modem.
What is needed is a method to monitor the line conditions in the data mode which is simple, independent, and transparent.
The ITU-T Recommendation V.34 (V.34 standard) is hereby incorporated by reference in its entirety.
It has been discovered that transmitting and monitoring a test signal in the data mode provides a method for a modem to monitor changing line conditions in the data mode.
More specifically, in one aspect of the present invention, a method for transmitting data over a network includes transmitting data over the network by a first modem. The data including a test signal. The method further includes receiving the test signal from the network by a second modem, comparing the test signal received by the second modem to a standard test signal, and selectively initiating retraining as determined by the comparison.
In another aspect of the invention, a modem includes a receiver for receiving signals from a network. Wherein in a first mode, the signals contain a first plurality of data originating from a computer system coupled to the network. The signals also include a first test signal within the first plurality of data. The receiver further includes a channel compensation module. The channel compensation module altering the signals received from the network to adjust for at least one condition of the network. The channel compensation module altering the signals as per a set of parameters. The set of parameters are reset as determined by a result of the receiver comparing the first test signal to a standard test signal.
Transmitting and monitoring a test signal in the data mode advantageously provides a way for the modem to monitor changing line conditions in the data mode that is simple, transparent and independent. Changing line conditions can be monitored with out noise averaging equipment or without the modems being compatible with the V.42 standard.